1. Field of the Invention
The present invention relates to an intermediate transfer belt, an image forming method, and an image forming apparatus using the intermediate transfer belt for use in electrophotography.
2. Discussion of the Related Art
In electrophotographic image forming apparatuses, seamless belts are used with various functions and uses, such as fixing belt, transfer belt, paper conveyance belt, and intermediate transfer belt.
Intermediate transfer belt is generally used in full-color electrophotographic image forming apparatuses. Toner images of cyan, magenta, yellow, and black each are transferred from a photoreceptor onto an intermediate transfer belt to form a composite full-color toner image thereon. The composite full-color toner image is then transferred onto a transfer medium such as paper.
Demand for intermediate transfer belt has grown in accordance with recent colorization of copiers. Intermediate transfer belts generally include materials such as thermoplastic resins, thermosetting resins, rubbers, and elastomers.
On the other hand, intermediate transfer belts are generally used in electrophotographic image forming apparatuses in which developing devices are arranged in tandem (hereinafter “tandem electrophotographic image forming apparatuses”) to increase printing speed.
In tandem electrophotographic image forming apparatus, intermediate transfer belt is required not to deform through image formation so as not to cause color drift. Intermediate transfer belt is also required to be strong and durable enough to withstand repeated use. Because intermediate transfer belt is also required to be flame-resistant, polyimide resins and polyamide-imide resins have been preferably used therefor. In particular, polyimide resins have been preferably used from the viewpoint of creep deformation property and durability.
In an electrophotographic image formation, some toner particles may remain on an intermediate transfer belt without being transferred onto a transfer medium. Therefore, a cleaning device for removing such residual toner particles from the intermediate transfer belt is needed.
One of the most effective ways to remove residual toner particles from an intermediate transfer belt is to scrape the residual toner particles off by pressing an edge of a cleaning blade against the surface of the intermediate transfer belt.
Intermediate transfer belt is generally provided with electric properties that are required for forming latent images and transferring toner images. However, the electric properties deteriorate with repeated image formation because the cleaning blade is constantly pressed against the intermediate transfer belt, shortening the lifespan of the intermediate transfer belt. As a result, abnormal images are likely to be produced.
Because of the widespread use of oilless fixing systems, recent toners typically include waxes and soft materials which are capable of being softened easily for the purpose of reducing the fixable temperature, which leads to energy saving. Such waxes and soft materials are likely to adhere to an intermediate transfer belt and are gradually formed into film with repeated image formation (this phenomenon is hereinafter referred to as “filming”), thereby degrading electric properties of the intermediate transfer belt.
Images are formed on not only typical copying papers but also coated paper and printing paper that include large amounts of loading materials such as talc, kaolin, and calcium carbonate. Loading materials are likely to adhere to an intermediate transfer belt when images are transferred from the intermediate transfer belt onto such papers and the adhered loading materials are likely to cause filming.
In attempting to suppress both the damage caused by pressure from the cleaning blade and the occurrence of filming caused by toner component materials and loading materials, one proposed approach involves reducing the surface friction coefficient of an intermediate transfer belt. For example, Japanese Patent Application Publication No. (hereinafter “JP-A”) 08-95455 and Japanese Patent No. 3753909 each propose a lubricant applicator for applying a lubricant to the surface of an intermediate transfer belt to reduce the surface friction coefficient thereof.
An image forming apparatus employing such a lubricant applicator is able to form high-quality images at low printing speeds. However, when the printing speed is increased in accordance with recent demand, abnormal images with undesired strips may be formed in continuous image forming operation. This is because a portion of the intermediate transfer belt on which an image exists has a higher surface friction coefficient than a portion on which no image exists, and therefore toner component materials and loading materials are likely to adhere to the portion on which an image exists, forming films thereon. In this case, little lubricant exists on the portion of the intermediate transfer belt having a higher surface friction coefficient. It is apparent from this fact that lubricant should be uniformly and reliably adhered to an intermediate transfer belt to form high-quality images at high printing speeds.
In attempting to adhere more lubricant to an intermediate transfer belt, one proposed approach involves roughening a surface of an intermediate transfer belt with abrasive paper, abrasive agent, etc., as described in JP-A 2005-316231 and JP-A 2004-361694.
JP-A 2005-316231 describes a method which forms concavities on an intermediate transfer belt in a circumferential direction by applying an abrasive agent to a circumferential surface of the intermediate transfer belt and rotating the intermediate transfer belt with an abrasive brush rotating in a direction parallel to the direction of conveyance of the intermediate transfer belt.
JP-A 2004-316194 describes a method which forms concavities on an intermediate transfer belt by abrading the intermediate transfer belt by setting it on an abrading mandrel.
These methods have a disadvantage that lubricant is likely to accumulate in the concavities. As a result, only a part of a surface of an intermediate transfer belt is supplied with the lubricant. There is another disadvantage that not only lubricant but also substances which may cause filming are likely to accumulate in the concavities. Additionally, toner images may be unevenly transferred from such an intermediate transfer belt due to the presence of the concavities.